oceanobob
Member
- Location
- central coast California
- Occupation
- electrical and industrial contractor company owner
Greetings:
Was wondering why a energized fluorescent light could cause a moderate tingle on the (additionally connected) metal gear case of a insulated right angle drill and not cause the circuit Ground Fault interrupter on the 120vac 20 amp outlet to activate?
Action: One of the extension cords was missing the grounding stab on the male end. Fixing this plug resolved this condition.
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Other actions and story to be told.
Testing* the GFI outlet (power source) showed no problem. The GFI outlet was replaced with a new one. This corrective action produced no change.
*Tested with a circuit tester and exercised the test/reset button.
The 'tingle' was felt when the drill case was held in one hand and the other hand inadvertently brushed against the steel gas piping. The gas piping was not completed fully as it was not connected to the service. A temporary jumper from the gas pipe to a nearby UFER ground caused the tingling to become significantly more noticeable. Operation of the drill had no effect on the observation; it simply needed to be plugged in. The drill has a three prong plug.
The construction work was being performed in a dried-in, wood framed, slab on grade dwelling unit. The temp power for the work was a 75 foot long 10ga molded end three prong extension cord plugged into a GFI protected convenience outlet at an adjacent occupied unit. That convenience outlet was supplied by a 20amp breaker and was the only purpose of that circuit.
The cord mentioned above had a three way molded 'pigtail tee' added to it. The workers were installing electrical rough in (type nm cabling) and were using a right angle drill to bore holes in the wood framing. The drill would be considered "new".
One leg of the tee went to the drill and the other leg of the tee went to the lights.
Two eight foot twin bulb flour lights were suspended from the ceiling to provide some additional lighting. The cords were connected to a three prong, three port 'tee' near the ceiling and this tee was being fed with a light duty short extension cord (infamous orange cord), and was plugged in to the molded power plug.
This 'orange cord' to the lighting tee was the one with the missing ground stab.
The drill, the lights, and a radio (of course! - but no talk show, only seasonally appropriate tunes this day).
There were no problems observed until the extension cord for the drill motor was unplugged from the molded power plug and plugged into that previously unused port on the (now named) "lighting tee".
I conclude the lights' ballast(s) were producing a potential on their metal housing - traveling from the housing through their three wire six foot SO cord to the 'tee' but was unable to travel further due to the missing prong on their supply orange extension cord. And since the lights weren't typically touched or contacted, the problem was undetected.
Until, that is, until the drill operator decided to plug the drill into the lighting tee - from this point the drill's gear case was connected to the metal housing of the problematic lighting. The potential was "only" felt while simultaneously touching the steel gas line and the drill gear case; once the steel pipe was bonded to the ufer ground, I suggest the situation was worsened due to less impedance to earth.
NOTE: Once those lights were bonded back to the source by repairing the plug on the now more infamous orange cord, no potential could be felt or measured.
Thank you in advance for your help with some questions:
1. How is it possible for the lights to produce the necessary energy to create a shock that is not discernible by the source GFI? The GFI did not activate/trip.
The person used the cord with the missing prong because of a belief: since the setup was on a GFI outlet, there shouldn't have been a problem.
1a Is it because the lights' transformer allows a transfer of energy from the primary circuit which is independent of the detection mode of the GFI?
2. Should these lights be tossed?
3. Should we consider special care when personnel are in contact with devices that use transformers which also have exposed metal parts?
v/r and Thanks.
Was wondering why a energized fluorescent light could cause a moderate tingle on the (additionally connected) metal gear case of a insulated right angle drill and not cause the circuit Ground Fault interrupter on the 120vac 20 amp outlet to activate?
Action: One of the extension cords was missing the grounding stab on the male end. Fixing this plug resolved this condition.
--------
Other actions and story to be told.
Testing* the GFI outlet (power source) showed no problem. The GFI outlet was replaced with a new one. This corrective action produced no change.
*Tested with a circuit tester and exercised the test/reset button.
The 'tingle' was felt when the drill case was held in one hand and the other hand inadvertently brushed against the steel gas piping. The gas piping was not completed fully as it was not connected to the service. A temporary jumper from the gas pipe to a nearby UFER ground caused the tingling to become significantly more noticeable. Operation of the drill had no effect on the observation; it simply needed to be plugged in. The drill has a three prong plug.
The construction work was being performed in a dried-in, wood framed, slab on grade dwelling unit. The temp power for the work was a 75 foot long 10ga molded end three prong extension cord plugged into a GFI protected convenience outlet at an adjacent occupied unit. That convenience outlet was supplied by a 20amp breaker and was the only purpose of that circuit.
The cord mentioned above had a three way molded 'pigtail tee' added to it. The workers were installing electrical rough in (type nm cabling) and were using a right angle drill to bore holes in the wood framing. The drill would be considered "new".
One leg of the tee went to the drill and the other leg of the tee went to the lights.
Two eight foot twin bulb flour lights were suspended from the ceiling to provide some additional lighting. The cords were connected to a three prong, three port 'tee' near the ceiling and this tee was being fed with a light duty short extension cord (infamous orange cord), and was plugged in to the molded power plug.
This 'orange cord' to the lighting tee was the one with the missing ground stab.
The drill, the lights, and a radio (of course! - but no talk show, only seasonally appropriate tunes this day).
There were no problems observed until the extension cord for the drill motor was unplugged from the molded power plug and plugged into that previously unused port on the (now named) "lighting tee".
I conclude the lights' ballast(s) were producing a potential on their metal housing - traveling from the housing through their three wire six foot SO cord to the 'tee' but was unable to travel further due to the missing prong on their supply orange extension cord. And since the lights weren't typically touched or contacted, the problem was undetected.
Until, that is, until the drill operator decided to plug the drill into the lighting tee - from this point the drill's gear case was connected to the metal housing of the problematic lighting. The potential was "only" felt while simultaneously touching the steel gas line and the drill gear case; once the steel pipe was bonded to the ufer ground, I suggest the situation was worsened due to less impedance to earth.
NOTE: Once those lights were bonded back to the source by repairing the plug on the now more infamous orange cord, no potential could be felt or measured.
Thank you in advance for your help with some questions:
1. How is it possible for the lights to produce the necessary energy to create a shock that is not discernible by the source GFI? The GFI did not activate/trip.
The person used the cord with the missing prong because of a belief: since the setup was on a GFI outlet, there shouldn't have been a problem.
1a Is it because the lights' transformer allows a transfer of energy from the primary circuit which is independent of the detection mode of the GFI?
2. Should these lights be tossed?
3. Should we consider special care when personnel are in contact with devices that use transformers which also have exposed metal parts?
v/r and Thanks.
